The known prior art consists in the methods and arrangements described and illustrated in International Patent Application PCT/SE85/00068 published under International Publication No. WO 85/3534.
The known methods and arrangements are effective in controlling shrinkage and/or stretch of a paper web during a web drying process, by subjecting the paper web to an outwardly directed force during that part of the drying process in which the web has a dry solids content of 75%, and in which the force applied is caused to act in the edge regions of the web.
This known publication proposes various methods for holding the edges of a paper web against the drying cylinders within the drying section during a web drying sequence.
The publication teaches to this end an arrangement which incorporates grooved edges and an arrangement which incorporates slalom wires, or S-wires, and in which a cylinder is provided with two peripheral rings which engage in grooves provided in the wire in a manner to force the web into the grooves. The publication also teaches an arrangement in slalom wires in which the paper web is pressed into and held in two grooves with the aid of strips, and also an arrangement in which edge straps are arranged on both sides of the web in the edge regions thereof and are adapted to hold the edges of the web against the cylinder via grooves formed therearound. The publication also teaches that the edge straps, or bands, can be held to and guided against the cylinder by means of two rings. Finally, the publication discloses an arrangement in which the edge straps are provided with longitudinally extending flanges, such that the flanges of two similarly located edge straps will co-act with and be held firmly against recesses formed in the periphery of the cylinder, preferably adjacent the end walls thereof.
The present invention can be said to be a further development of this latter arrangement.
It will be apparent from the aforegoing that the prior International Application illustrates a plurality of different embodiments for applying oppositely directed forces to the edge portions of a paper web as it passes through the drying sections.
When studying the measures taken to this end it will also be seen that a qualified technical problem resides in the provision of conditions, with the aid of simple means, which will enable the respective edge portions of a paper web to follow a pre-determined path throughout the whole of the drying section, or if so desired throughout a part of said section, and then the forwardly located part of said section, and therewith create conditions for controlling and establishing the extent of web shrinkage and/or web stretch at right angles to the direction of web travel as the web passes through the drying section, thereby realizing the technical advantages recited in the aforesaid publication.
It will also be seen that a technical problem resides in the simple provision of a strap which, while effectively solving the aforesaid technical problem, is of simple construction and cheap to produce.
A further technical problem resides in the provision of a strap which, within reasonable limits, is able to eliminate the risk of accidents at high web speeds.
A related technical problem is one of providing with the aid of simple means conditions for ensuring that the edges of the paper web are firmly held to the strap.
Another technical problem will be seen to exist in creating, with the aid of simple means, conditions which enable the respective edge portions of the web to adhere to the straps through an adhesive layer, preferably applied to one side thereof, and to provide with the aid of simple means conditions for controlling the orientation of the strap through the drying section.
It will also be seen that a technical problem resides in the provision of conditions, with the aid of simple means, with which the adhesive force of the adhesive layer can be made so effective as to resist occurrent tensile forces, preferably forces that occur as a result of the tendency of the web to shrink and/or its inclination to stretch, but which, at the same time, will allow the mutually co-acting edge portions and strap to be separated from one another upon completion of the drying process.
A further technical problem in this regard is one of providing a strap arrangement which can be adapted readily for adhesive co-action with a paper web and which is suitable for use in a drying section of the aforesaid kind.
Another technical problem resides in the provision of a strap which can be incorporated readily in an existing drying section.
It will also be seen that a further problem is one of creating in an existing drying section, with the aid of simple means herefor, conditions which will enable one or more adhesive layers to be applied continuously to either the strap or the edge portions of the paper web.
Another problem in the present context is one of establishing how wide the adhesive layer must be in order to resist the forces that occur while, at the same time, enabling the strap to be parted readily from the web upon completion of the web drying process; a particular problem in this regard is one of enabling the adhesive layer to hold a paper web firmly to a hot elastic strap which has planar surfaces.
It will also be seen that a technical problem resides in the provision of a strap which is suitable for the aforesaid purpose.